Appliance for grinding the contact points of contact breakers



Dec. 5, 1950 P s PA ET 2,532,512

. G APPLIANCE FOR GRINDING THE CONTACT POINTS OF CONTACT BREAKERS Filed Oct. 10, 1949 4 N m VEn Tae 1 Pin-PA GE? Patented Dec. 1950 APPLIANCE FOR GRINDING THE CONTACT POINTS OF CONTACT BREAKERS Peter Samuel Paget, Mangotsfield, near Bristol,

England Application October 10, 1949, Serial No. 120,449 In Great Britain October 12, 1948 v1 Claim.

This invention relates to apparatus for grinding the contact points of contact-breakers such as used for internal combustion engines. Contact-breakers, when received from the manufacturers often suffer from the disadvantage that the contact faces of the points are not true, causing undue pitting and wear and causing arcing and rapid burning of the points and lowering the efiiciency of the electrical apparatus in which the contact breaker is fitted. Also some new contact points have pips in the centre and/or are badly scored and therefore produce the above mentioned disadvantages.

5 Also during service said contacts suffer pitting and corrosion due to the sparking at the points. It is necessary from time totime to re-surface the points, therefore the apparatus according to the invention will enable this to be done.

The object of the invention is to provide an appliance to grind or dress the contact faces of the points of a contact-breaker in an expeditious manner and to ensure true and correct mating thereof and smooth faces and so maintain the efliciency of the electrical contact.

A further object of the invention is to provide such an appliance which is simple and inexpensive to construct.

According to the invention the appliance for grinding the contact faces of contact-breakers comprises a stand having an emer or like grinding wheel rotatably mounted thereon and adapted to support one or more rotatable carrier members each having a plurality of pins for selective engagement with a contact-breaker and means for locking said carrier member against rotation whilst the contact-breaker pivoted on one of said pins is pressed into contact with said grinding wheel.

The operative face of the grinding wheel may be fiat whereby fiat faces are imparted to the contact points, but with points so treated there is only one position in their adjustment in the contact-breaker at which they will face each other squarely, as if the adjusting screw of the points is moved only a fraction of a turn either way the points will then touch only on the rim.

It is therefore preferred to impart a slight convexity to the points as they can then be adjusted within quite a wide range whilst still retaining a good area of contact.

In consequence it is therefore preferred to employ a grinding wheel having on its operative face a slight concavity whereby a slight convexity will be imparted to the said points.

A preferred form of such grinding wheel com.-

2 prises a face plate having a slight concavity on one face and a flexible abrasive disc mounted on such face so as to conform to such concavity.

For grinding the stationary screw type and similar kinds of contacts of contact-breakers a separate carrier member may be combined with the appliance.

In order that the invention may be clearly understood and readily carried into effect a preferred form of the invention will now be described by way of example and with reference to the drawings accompanying the present specifica tion. In the drawings:

Fig. l is a perspective view of the apparatus in its latest form.

Fig. 2 is a part sectional side elevation drawn to a larger scale: and

Fig. 3 is a plan view.

Referring to the accompanying drawings the appliance comprises a main body or stand consisting of a casting, turning or fabrication of some suitable alloy, and which supports in bearings a spindle A which carries a face plate B to which is bolted a flexible grinding disc C, which is conveniently made of sand or other abrasive paper.

In order to give a slight degree of convexity to the points being ground and so ensure that worn contacts will retain a good area of contact through quite a wide range of adjustment, the face plate B is slightly concave on the side to which the flexible abrasive disc C is attached, whereby the said disc will adapt itself to and will acquire the concavity of the face plate. Thus a slight convexity is imparted to the points by (a) the drag on the abrasive disc, which drag, owing to the flexibility of the disc, causes it to build up on either side of the point being dressed and (b) the slight radius of the disc which gives a corresponding radius to the contact point. Thus a radius is given to the point in two directions in the same plane, each at right angles to the other which in effect gives the desired degree of convexity.

The stand supports a pair of carrier members F and G of disc form provided with axial pins D and E by means of which they are rotatably mounted in side extensions S of the stand S. The carrier members F and G are fitted with a plurality of upright pins H. J. V. K. X. W., which act as pivot centres for the various types of contact-breakers, the pin being selected which will lit the fulcrum point of the contact-breaker under treatment.

The said pins H. V. 8; W, may be screw threaded 3 to receive knurled nuts Z for retaining certain types of contact-breakers in position during grinding.

Keeper pins L and M respectively are used to prevent the carrier members F and G from turning during grinding. The keeper pins L and M being inserted in the selected one of anurnber 0f holes Y in the carriers "F and G'and the projecting lower ends of the pins L and M entering one of a number of locating holes suitably arranged in the parts S of the stand. In this, manner different kinds of contacts can be pivotally mounted on appropriate pins so that the contacts R are correctly positioned in relation to the abrasive disc C. Other suitable locking means may-- however be employed for retaining the members F and G against rotation during grinding.

A loose carrier member N tapped to receive the stationary screw type contact of a contact 'b'reak er is slidably fitted in an arm 0 forming part of the stand and can be used to applyvthe contact against the face of the grinding disc C, by pressing the member N towards the abrasive disc byhand or in any other suitablemanner.

. The invention is not limited to the precise form of'carrier member F or G illustrated in full lines in Fig. 1 of the drawing but auxiliarycarrier members F and Gfi'as. diagrammatically shown by the chain; dot in- Fig. 3 may be mounted on the main carrier members Fand G to accommodate various American and other type contact-breakers which cannot be accommodatedon the carrier members F and G owing to, their peculiar hap t In operation of the grinding appliance a contact-breaker P is. mounted on the correct pivot pin of the carrier members and the latter locked in position by the keeper pinL; or The face of the contact point R.. v is pressed against the grinding disc C by hand or in any other suitable manner whilst the. discs B. Q. are rotated by a handle T until the contactfac is properly clean and convex. v

The complementary stationary contact point of the breaker is mounted in the. loose carrier member N, already referred to, which is then. in-

troduced through the arm 0. and pressed; against the grinding disc C,v or alternatively mounted on pins provided on carriers F or G.

f From the foregoing it will beseen thattheinvention provides means by which the contact arms are in effect jigged. so. that. the angle at stances there is no tip left.

4 which the contacts are ground is an exact copy of the angle at which they will lie when placed in the distributor housing. Thus under all conditions the contacts having been dressed on the apparatus will mate up correctly and square to each other. The points may also be ground at a correct angle which varies with .difierent points and with difierent stages of wear and which angle would be impossible to predict without the form of; jigging provided by the present invention.

Another advantage of the present invention is that the. very vminimum of metal i removed from the point which is not so when points are filed by hand aswith hand work the points often have a .la'rge amount of metal removed through correcting errors often cumulative, until in some in- The fact that both new points and used points may be correctly aligned on the apparatus is particularly desirable, especially in the case of new points.

Provision may be made for adding suitable brackets, bushes and so on to accommodate other types of points such as those used in cut outs. petrol pumps, starters and the like.

I claim:

An appliance for grinding the contact faces of contact breakers comprising a stand, at least one carrier member having a plurality of pins for selective engagement with a contact breaker rotatably mounted on said stand, means forlocking said carrier member against rotation in anyone of a number of predetermined positions and a grinding wheel rotatably mounted on. said stand; said grinding wheel comprising a. face plate having a slight concavity on one face and a flexible abrasive disc mounted on. said face so as. to conform to the concavity thereon, whereby a slight degree of convexity is imparted to the/contact face being ground.

PETER SAMUEL PAGET.

REFERENCES GI 'I'ED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,429,80l Ifhomas Sept. 19',;1922 1,973,479 Stocker Oct. 30', 1934 2,374,601 K6115 Apr. 24, 1945 2,474,086 Bartlow June21, 1949. 

